The washer and dryer were removed to the living room, the floor was tiled, then the washer brought back in for some laundry and removed again. The bathtub was installed, leveled, plumbing added, then drywalled. There is no such thing as waterproof drywall, just moisture and mold resistant, but any material will fail if the job is not sealed properly. Here I'm installing the green drywall 1/8" above the tub. The gap and corners are filled with silicone. The rest is finished with a chemical setting compound powder (Durabond, CertainTeed 90, etc.) that is mixed with water. The surface is then primed and painted with several coats of high quality acrylic paint and left to cure. It is now waterproof and could even be used as is, but with a proper tile job and waterproof sealing grout, it should last for many years, as jobs I did many years ago, have lasted.

Since I wanted a custom vanity, 20½" X 8' I had to build my own.  The black 3" wall piece was cut from the 25" countertop to make it 22", as narrow as possible and still fit the sinks.  I just used leftover pieces of wood and 1/4" Masonite shipping panels, (free from Lowes) used for the floor and end side.  I also glued them to 1/2" plywood shipping panels (free) to make the four doors.

I didn't have enough extra wood to build the two 30" X 30" cupboards, and the 2021 prices made it more feasible to just buy them ready made (with "soft close" hinges) from Lowes.  Tip - if you're buying "soft close" hinges for existing "regular close" doors, they could be strong enough that you may only need to replace one hinge per door, therefore costing half as much.  

I found that two "soft close" hinges were too strong and closed too slowly.  One "soft close" and one "regular close" hinge per door, closed at just the right speed.

 

I custom built the mirror frame (right). Since it was mounted on top of the tiled splash (two feet above the three foot high vanity) the bottom of the mirror was over five feet high, so you would have to be over 5'8" just to see your face.  By tilting it forward 15°, anyone from ~ 4'8" to 7'8" can easily use it.  If you wanted even shorter people to see themselves, just tilt it to ~20°.

"People should pursue what they're passionate about. That will make them happier than pretty much anything else." Elon Musk

If you have two yardsticks, here's a way to accurately measure the distance between two inside walls - for the installation of a custom made shelf above the washer and dryer.  Just add 36" + 19⅛" to get 55⅛". Note, that you can flip, top to bottom, the "yardsticks" to measure metric. (91½ + 48½ = 140cm)

Because the mirror tilted forward, there was an unwanted triangular space behind it that might catch any objects accidentally thrown up into it, so I made a top Masonite cover which just needed two screws to hold it down.  They needed two pilot holes, but there was no way to drill the holes with only 5½ inches of space.  Even my Angle Drill needs 7¼ inches.  My angle grinder is 4½ inches but if I had

machined a custom threaded adaptor, plus the drill bit, it would have needed about the same space as the Angle Drill attachment.

 

I decided to build a complete custom electric drill using my RC motors,  batteries and electronics, above.  They were "velcroed"

and "cable tied" to a large paint stick.  Being only 4¾" deep, it easily fit into the space and handily drilled the holes.  Then the screws were effortlessly screwed in with my Stubby Robertson.

Below - The toilet is semi private behind the bath enclosure wall, barely sticking out in the middle pic. and there is a shelf above it.  The shelf above the washer & dryer, along with the bottom and top vanity cupboards, provide a copious quantity of storage space.  The glass door handles can also double as towel racks.

(plus some "Build Your Own Vanity" tips)